On the global scale, energy is abundantly used for cooling, opposing the natural tendency of thermal energy to pass towards a cooler object. As the climate warms up, cooling and dehumidification will require more energy.
Conventional compressor cooling is a highly power consuming/energy demanding method. Absorption cooling among other things takes efficient advantage of waste heat. The thermoelectric unit based on the Seebeck phenomenon converts heat into electricity, however, it has high production costs, thus becoming inappropriate for objects requiring larger amounts of energy.
In addition to buildings, vehicles and industrial processes, temperature control is also vital in heat-generating devices, such as computers.
Ventilation is important, but often it is impossible to use, for example, in places with polluted air, such as in shops on the street level. In many applications, like cooling of computers, ventilation is unnecessary.
In a PCM heat storage, known per se, material phase changes are generally between a solid state and a liquid state. Such storages are usually maintained in the temperature range 0-100° C., thus being suitable for short-term energy storage when connected to heaters and coolers. Typical media comprise water/ice, salt brines, inorganic salt hydrates, saturated hydrocarbons and fatty acids of high molecular weight. PCM storage units have the benefits of a small size, compared e.g. to storage units for water alone, and do not have any moving parts. PCM materials have recently been utilised for the heating and cooling of cloth used for wearing apparel. One drawback of PCM storages is caused by their poor heat conductivity. PCM storages can also be given a plate-like shape. Heat discharges from the PCM storage constitute a major problem, because further heat cannot be stored unless it has first been discharged. The PCM operation is thus based on cyclic charges and discharges. One of the advantages of PCM materials is their operation with small temperature differences. If the temperature between outdoor and indoor air of ventilation is same, of course phase change does not take place.
The cooling demand in buildings depends on three components: the heat load caused by outdoor air, by indoor air and by ventilation. Heat recovery operating on the counter-current principle has proved to yield higher efficiency than a system operating on the forward-current principle (See e.g. U.S. Pat. No. 7,059,385). In a regenerative system, heat is stored effectively in heat recovery cells.
In recuperative cross-current plate heat exchangers, air currents are not reversed, and hence they cannot interact optimally with a PCM storage nor with a regenerative rotating heat recovery cell.
A stationary, regenerative and accumulating storage cell system operating on the counter-current principle is straightforward and effective. The cell system may be made of any material having high thermal storage (heat capacity), such as aluminium or copper. Also one rotary type regenerative heat exchanger can be used that alternately rotates between two counter (air) flows, thereby substituting for two heat exchanger cells, although efficiency is lower and the construction quite complicated and expensive.
A vortex tube or similar device, known per se, takes advantage of the Venturi phenomenon. The vortex tube has one inlet port and first and second outlet ports at opposite ends of a tube arranged perpendicular to the inlet port. A compressible fluid such as air enters the inlet port and heated air exits the first outlet port while cooled air exits the second outlet port. The vortex tube has no moving parts. For example, if 21° C. air enters the inlet port, 76° C. air can exit the first outlet part and −34° C. can exit the second outlet port.
Instead of vortex tube, conventional technology such as a compressor can be used to create a thermal difference, but then the efficiency is lower. If the vortex tube is used alone, the capacity is typically not economical for cooling/heating large spaces.
In patents DE 3825155, U.S. Pat. No. 4,407,134 and published US application US 2002073848, a vortex tube is mentioned as a separate device used for production of a cool air stream on one side and a hot air stream on the other side. This tube is also not connected to any heat exchanger either with the PCM or without, because its continuous principle of operation does not allow the vortex tube to be connected with a device which operates periodically, as in the present invention. In EP 1455157 PCM is mentioned as a heat storage media only, but it is not connected to an external vortex tube unlike the present invention.